BGE: How to create a countdown timer without using debug or python?
You can add a game property to an object, of type "Timer". For my BGE project, I created an Empty named "Clock", just for this purpose. It has one game property "GAME_TIME", as shown on this screenshot:



You can use this property to keep track of time, as it'll increase as long as the game is running. You can also set it to 0.0 to restart the timer.